#include <stdio.h>
#include <string.h>
#include <math.h>

long long mod_exp(long long base, long long exp, long long mod) {
    long long result = 1;
    base = base % mod;  

    while (exp > 0) {
        if (exp % 2 == 1) {  
            result = (result * base) % mod;
        }
        base = (base * base) % mod;  
        exp = exp / 2;  
    }

    return result;
}

long long codifica(long long m, int e, int n) {
    return mod_exp(m, e, n);  
}

long long bloco_para_numero(char bloco[], int tamanho) {
    long long numero = 0;
    for (int i = 0; i < tamanho; i++) {
        numero = numero * 36 + (bloco[i] - 'A' + 10);  
    }
    return numero;
}

int main() {
    char mensagem[100]; 
    int p, q, e, tamanho;

    printf("Digite a palavra que você quer codificar, em letras maiúsculas\n");
    scanf("%s", mensagem);

    printf("Digite os dois números primos 'p' e 'q' (na forma 'p q')\n");
    scanf("%d %d", &p, &q);

    printf("Agora, digite o número 'e' e o tamanho do bloco 't' (na forma 'e t')\n");
    scanf("%d %d", &e, &tamanho); 

    int n = p * q; 

    int mensagem_len = strlen(mensagem);

    printf("A mensagem codificada é: ");
    for (int i = 0; i < mensagem_len; i += tamanho) {
        char bloco[tamanho + 1];
        int j;
        
        for (j = 0; j < tamanho && (i + j) < mensagem_len; j++) {
            bloco[j] = mensagem[i + j];
        }
        bloco[j] = '\0';  

        long long numero_bloco = bloco_para_numero(bloco, j);

        long long codificado = codifica(numero_bloco, e, n);

        printf("%lld", codificado);
        
        if (i + tamanho < mensagem_len) {
            printf(" - ");
        }
    }
    printf("\n");

    return 0;
}
by

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Read inputs from stdin

OneCompiler's C online editor supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample C program which takes name as input and print your name with hello.

#include <stdio.h>
int main()
{
    char name[50];
    printf("Enter name:");
    scanf("%s", name);
    printf("Hello %s \n" , name );
    return 0;
    
}

About C

C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.

Key features:

  • Structured Programming
  • Popular system programming language
  • UNIX, MySQL and Oracle are completely written in C.
  • Supports variety of platforms
  • Efficient and also handle low-level activities.
  • As fast as assembly language and hence used as system development language.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition if-else is used.

if(conditional-expression) {
   // code
} else {
   // code
}

You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to if-else-if ladder.

switch(conditional-expression) {    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
...    
    
default:     
 // code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  // code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while(condition) {  
 // code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {
  // code 
} while (condition);

Arrays

Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.

Syntax

One dimentional Array:

data-type array-name[size];

Two dimensional array:

data-type array-name[size][size];

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

Two types of functions are present in C

  1. Library Functions:

Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,

  1. User defined functions:

User defined functions are the ones which are written by the programmer based on the requirement.

How to declare a Function

return_type function_name(parameters);

How to call a Function

function_name (parameters)

How to define a Function

return_type function_name(parameters) {  
  //code
}